Esther Rantzen: "I am very concerned that we are losing sight of the real problem"
Rules to vet parents who regularly drive children for sports or social clubs have provoked fierce criticism.
Along with parents who host foreign exchange students, they will fall under the Vetting and Barring Scheme.
Opposition parties have attacked the plans and campaigner Esther Rantzen said they showed a "loss of perspective".
But the government said its goal was child safety and the Children's Society said sharing information was vital.
The measures are being introduced from next month in England, Wales and Northern Ireland.
A separate but aligned scheme is being set up in Scotland, to be introduced next year.
Also, anyone barred in any part of the UK will be barred from working with children and vulnerable adults anywhere else.
Under the scheme, parents who are not vetted will be subject to a fine of up to £5,000.
Informal arrangements between parents will not be covered, but anyone taking part in activities involving "frequent" or "intensive" contact with children or vulnerable adults three times in a month, every month, or once overnight, must register, it has emerged.
The government's Vetting and Barring Scheme is a child of moral panic
All 300,000 school governors, as well as every doctor, nurse, teacher, dentist and prison officer will also have to sign up.
It is thought that 11.3 million people in England, Wales and Northern Ireland - close to one in four of all adults - may register with the Home Office's Independent Safeguarding Authority [ISA].
According to BBC home affairs editor Mark Easton it is thought out of that 11.3 million, "something will come up", such as a conviction, for about one million.
"Of those million, they reckon 40,000 will be told they are unsuitable to work in those regulated areas," he said.
After November 2010 failure to register could lead to criminal prosecution and fine. The clubs themselves also face a £5,000 penalty for using non-vetted volunteers.
Children's minister: "Safeguarding children is a number one priority"
Moira Murray, head of safeguarding at the Children's Society, said: "I think we have to ask the question 'what could be better than ensuring that those who are working with children are safe and that children are protected from people who want to work with children, who shouldn't be working with children, who have other motives for working with children?'"
The scheme has come under fire from opposition parties.
Shadow home secretary Chris Grayling said the regime had the potential to be a disaster.
"We are going to drive away volunteers, we'll see clubs and activities close down and we'll end up with more bored young people on our streets.
Liberal Democrat home affairs spokesman Chris Huhne said the government was "in danger of creating a world in which we think every adult who approaches children means to do them harm".
And Ms Rantzen said the whole population was being "blanketed with this extraordinary suspicion that they might be a danger to children."
She told the BBC she was also worried that the checks might "take account of rumour, gossip, unfounded allegations which may be recorded on the police computer."
But children's minister Delyth Morgan said: "It is about ensuring that people in a position of trust that work frequently and intensively with children are safe to do so.
"Ultimately safeguarding children is the government's priority."
John O'Brien, programme director of the Vetting and Barring Scheme, said it would be a "once-only, simple step". He denied it was a "presumption of guilt".
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.